In intercoolers employed in multi-stage centrifugal compressors, as well as in other related heat exchangers, gas introduced into the heat exchanger is caused to pass over coolant containing tubes whereby heat is transferred from the gas to the coolant with the gas being subsequently emitted through a discharge outlet.
One known embodiment of heat exchanger of the above-described type is disclosed in U.S. Pat. No. 4,415,024. An elongated cylindrical shell is provided with a gas inlet and a gas outlet and a rectangularly-shaped array of coolant tubes contained within a tube bundle. The tube bundle is fixedly attached to tube sheets at opposite ends of the shell. Typically, one tube sheet is rigidly held against the shell assembly by a fixed header assembly and the opposite tube sheet is connected to a floating header assembly which is allowed axial movement with respect to the shell assembly to allow for thermal expansion of the tube bundle relative to the shell assembly. The rigidly held tube sheet is provided with a gasket to seal between the tube sheet and shell assembly. The floating tube sheet and header assembly is usually provided with an O-ring seal to seal between the sliding header assembly and shell assembly flange. The coolant is introduced into the header assemblies to provide a flow of coolant through the tube bundle to cool the gas circulating through the shell assembly.
However, this design has certain limitations and is not particularly well suited for high shell pressure use. The sealed connections between the tube bundle and tube sheets can leak due to thermal stresses therebetween and/or by the interaction of the high pressure gas within the shell assembly acting on the tube sheet and seals. If leakage occurs, the gas and coolant mediums will be mixed thereby causing contamination of the mediums. Furthermore, the gasket between the floating header assembly and tube sheet can leak, providing an alternate contamination path mixing the two mediums.
It is, therefore, desirable to provide a heat exchanger assembly having a pair of tube sheets at each end of the tube bundle, the pair of tube sheets being spaced with said space being communicated exteriorly of the heat exchanger. Heat exchangers utilizing such a dual tube sheet design are not necessarily new in the industry. U.S. Pat. No. 2,152,266 to McNeal shows a heat exchanger utilizing dual tube sheets as described above. However, there is no provision contained therein limiting the axially expansion of the floating header assembly. In high shell pressure applications it is necessary to provide a counteracting force on the outer side of the floating header assembly and tube sheet to prevent the tube bundle from excessive axial movement due to internal shell pressure forces which can create harmful stresses between the tube bundle and tube sheet thereby breaking the fluid-tight container connections therebetween.
U.S. Pat. No. 1,962,170 to Blemerhassett shows a dual tube sheet design for a heat exchanger further utilizing a pressure balancing means to prevent pressure from within the shell to overly expand the tube bundle. This is accomplished by totally enclosing the floating header assembly and tube sheet within the shell to allow the high pressure fluid within the shell to act upon all sides of the floating assembly. However, to accomplish this and provide for dual tube sheets, a complex passage system must be provided to vent the space between the dual floating tube sheets. Furthermore, it is impossible to remove the floating header assembly from the tube sheet to clean or inspect the tube bundle without exposing the main shell casing to contaminates. And, if the gaseous medium is corrosive, a multiplicity of parts relating to the floating header assembly are subjected to corrosion and possible premature failure.
There remains a substantial need for an efficient heat exchanger such as shown in U.S. Pat. No. 4,415,024 which maintains the advantages described therein and which is adapted for use as a high pressure intercooler in centrifugal compressors, as well as in other environments, wherein double tube sheets are provided between the shell assembly and header assemblies providing a space therebetween to allow leakage from either fluid medium to escape exteriorly of the intercooler. Additionally, it is desirable to counter-balance the high pressure forces existing within the shell cavity acting on the floating tube sheet to prevent undue axial expansion of the tube bundle and floating tube sheet.